1. Field of the Invention
The present invention relates to a loudspeaker, and more particularly to a loudspeaker for use in a variety of types of audio apparatuses, for example, an audio and visual apparatus.
2. Description of the Background Art
Conventionally, an audio and visual apparatus, such as a television, is configured so as to include loudspeakers on opposite sides of a cathode-ray tube. Accordingly, as the loudspeakers for use in the audio and visual apparatus, loudspeakers structured in an elongated shape, such as a rectangle, an ellipse, etc., are used. In recent years, as a display screen becomes wider, the loudspeakers for use in the audio and visual apparatus are required to become narrower, and also required to become thinner so as to be adapted to an apparatus with a thin depth, such as a liquid crystal display or a plasma display.
Here, a conventional loudspeaker with an elongated structure is described with reference to FIGS. 17 through 19. FIG. 17 is a plan view of the conventional loudspeaker with an elongated structure, FIG. 18 is a cross-sectional view of the loudspeaker in a long axis direction, and FIG. 19 is a cross-sectional view of the loudspeaker in a short axis direction. In FIGS. 17 through 19, a diaphragm 1, which creates air vibration, has an elongated shape, and an outer circumference of the diaphragm 1 is supported to a frame 3 via an edge 2. A voice coil 4 is fixed on a planar portion of the diaphragm 1.
The frame 3 includes in its center a magnetic circuit 8 consisting of a yoke 5, a magnet 6, and a top plate 7. In FIG. 19, the magnet 6 is magnetized in a direction perpendicular to the diaphragm 1 (i.e., a direction of arrow Z shown in FIG. 19). Accordingly, a magnetic gap 9, where magnetic flux is generated in a direction perpendicular to the diaphragm 1, is formed between an opening of the yoke 5 (in the vicinity of the edge 2) and the top plate 7. The voice coil 4 is located within the magnetic gap 9 in a direction perpendicular to the magnetic flux (i.e., a direction perpendicular to the sheet of FIG. 19). Accordingly, if an alternating current is applied to the voice coil 4, the diaphragm 1 is caused to vibrate in the direction of arrow Z shown in FIG. 19, thereby emitting sound waves into space.
In a conventional loudspeaker, a voice coil is bonded to a planar portion of a diaphragm by an adhesive. Each wire of the voice coil has a circular cross section, and therefore an area of contact between the voice coil and the diaphragm is small. Also, the adhesive is easily spread into a thin sheet over the diaphragm, and therefore an adhesive layer made of the adhesive becomes thin. Due to the small contact area and the thin adhesive layer, adhesive strength between the voice coil and the diaphragm is small. Accordingly, the diaphragm and the voice coil are separated from each other, resulting in an increase in distortion of the diaphragm during vibration or causing insufficient vibration.
Note that, particularly in the loudspeaker with an elongated structure, the diaphragm is easily distorted during vibration, and therefore it is required to increase the adhesive strength between the diaphragm and the voice coil. Also, in a voice coil having a horizontally-elongated cross section (i.e., if a vibration direction of the diaphragm corresponds to a vertical direction, the cross section of the voice coil is short in the vertical direction and long in the horizontal direction), if the adhesive strength between the voice coil and the diaphragm is small, wires of the voice coil might be separated from each other due to the vibration of the diaphragm. If the wires of the voice coil are separated from each other, reproduction sound quality is reduced.